Electron beam welding behavior in Eurofer subjected to the PbLi eutectic

Abstract

The weldability of Eurofer steel and the behavior of weld beads under relevant fusion conditions are critical factors to assess for future designs, specifically in the context of the Water-Cooled Lithium Lead (WCLL) blanket concept. Here, the area corresponding to the breeder blanket will be in direct contact with the PbLi eutectic alloy, which will flow continuously at temperatures between 400 °C and 550 °C. In this study, electron beam welding was performed on 1.4 mm thick Eurofer plates. These welded samples were subsequently exposed to flowing PbLi in the CiCLo loop at CIEMAT, maintained at 450 °C for 1000 h.

Prior to corrosion testing, the microstructure of the samples was characterized to evaluate the fusion zone width, bonding coefficient, and the presence of any defects or brittle joints. Acicular delta ferrite was observed, attributed to the high temperatures during welding and rapid cooling afterward. The potential for improved corrosion resistance through normalization treatment post-welding was also assessed. Following PbLi exposure, the specimens underwent the same microstructural characterization.

The results showed a significant microstructural change in the HAZ, which caused an increase in hardness in the HAZ; this result occurred in both the as-welded and heat-treated materials. It should be noted that non-negligible amounts of lithium were found in the HAZ, which is evidence of the diffusion of lithium from the molten eutectic into the interior of the material.